The present invention relates generally to a control apparatus for controlling a system of an automotive vehicle in response to sensed dynamic behavior, and more specifically, to a method and apparatus for controlling the system of the vehicle by determining attitude of the vehicle.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the roll over characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle rollover control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
It is well-known in aircraft and spacecraft attitude control to use gyro-rate sensors to control the attitude of the aircraft and spacecraft in a rather complicated fashion. The direct integrations of the gyro-rate sensor signals does not provide the actual attitude of the aircraft and spacecraft due to the fact that a large portion of the motion involve 3 dimensional maneuvers, and in those 3-D maneuvers the motion variables are inter-dependent with each other.
The vehicle dynamics control tries to control the yaw stability and roll stability of an automotive vehicle. The task involves three-dimensional motions along its roll, pitch, yaw directions and its longitudinal, lateral and vertical directions. The coupling between the motion directions may not be as strong as in the aircraft and the spacecraft, however they cannot be neglected in most of the maneuvers which involve vehicle rolling over or yawing out of the course. For example, the excessive steering of a vehicle will lead to excessive yaw and lateral motion, which further cause large rolling motion towards the outside of the turning. If the driver brakes the vehicle during the excessive steering, then the vehicle will also experience roll and pitch motions together with lateral and longitudinal accelerations.
In known systems the interdependencies are typically not taken into account. Also, such systems do not provide accurate indications of roll tendencies over large periods of time. That is, when integrations of the sensors are performed, only short term integrations are performed. However, in ramp maneuvers or long curve maneuvers results by such systems have proven inaccurate.
It would therefore be desirable to provide an attitude control system to predict attitude angle for vehicle dynamics control that includes the interdependency among the roll, pitch and yaw motions while compensating for long term maneuvers.
In the present invention, the interdependency among the vehicle roll, pitch and yaw motion variables is characterized by a set of nonlinear differential equations through the well-known Euler transformation. That is, the roll, pitch and yaw attitude angles of the vehicle are related to the roll, pitch and yaw rates through three nonlinear differential equations. Solving those differential equations numerically theoretically leads to the variables of interest. However, a numerical integration for solving the nonlinear differential equations causes signal drifting. In order to solve this problem, a new integration scheme is proposed. This scheme combines the anti-integration-drift filter with the steady-state value correction to provide true vehicle attitudes.
Reducing system cost is typically a goal in automotive systems. Since one of the three angular rate signals (pitch rate signal) can be predicted from the other available signals, the cost reduction of the system is possible by eliminating a pitch rate sensor.
In one aspect of the invention, a control system for an automotive vehicle includes a plurality of sensors sensing the dynamic conditions of the vehicle. The sensors may include a speed sensor 20, a lateral acceleration sensor 32, a roll rate sensor 34, a yaw rate sensor 26 and a longitudinal acceleration sensor 36. The controller 26 is coupled to the speed sensor 20, the lateral acceleration sensor 32, the roll rate sensor 34, the yaw rate sensor 28 and a longitudinal acceleration sensor 36. The controller 26 has an anti-integration drift filter and a steady state recovery filter. The controller determines a roll attitude angle, a pitch attitude angle, a yaw attitude angle and a pitch rate in response to the roll angular rate signal, the yaw angular rate signal, the lateral acceleration signal, the longitudinal acceleration signal, the wheel speed signal, the anti-integration drift filter and the steady state recovery filter.
In a further aspect of the invention, a method of controlling roll stability of the vehicle comprises the steps of:
generating a plurality of sensor signals in response to vehicle conditions;
estimating a vehicle pitch angle estimation in response to said plurality of sensor signals;
determining a transient roll attitude in response to said pitch angle estimation;
determining a steady state roll attitude angle in response to said pitch angle; and
determining a roll attitude angle estimation in response to the steady state roll attitude angle and the transient roll attitude angle; and
determining a pitch rate estimation in response to the estimated roll and pitch angle estimation, and the yaw rate sensor signal.
One advantage of the invention is that the above methodology may be applied to eliminating another sensor corresponding to roll or yaw while providing a sensor corresponding to pitch.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.